Reference Microsoft.NETCore.Platforms where necessary.

test/ServerComparison.FunctionalTests/project.json

@@ -9,6 +9,7 @@
     "Microsoft.AspNetCore.Server.Testing": "1.0.0-*",
     "Microsoft.Extensions.Logging.Console": "1.0.0-*",
     "Microsoft.Net.Http.Headers": "1.0.0-*",
+    "Microsoft.NETCore.Platforms": "1.0.1-*",
     "xunit.runner.aspnet": "2.0.0-aspnet-*"
   },
   "frameworks": {